"...star images were taken during the interplanetary cruise and also while orbiting Mars to determine and then monitor other geometric properties of the cameras. The narrow angle camera had a detection threshold of 9th visual magnitude, enabling at least a few stars to be imaged in any long exposure picture. Focal lengths and relative camera alignments were computed from the star images and were found to be stable to an accuracy of a pixel throughout the mission."

Of course, that was before all the fun with Hubble!

You'd think, though, that after Hubble, and MCO, and Genesis there's be a sorta checklist cum diary on each of the mission staff's desks - you know, things like:

* Fix Focus by Friday* Go Metric on Monday* Set pyros after Sunday (AKA This Way Up on Wednesday!)

Well, I'd bet $10 that the pixels now are at least an order of magnitude smaller, if not more, than the pixels for Mariner 9. I'd bet $1 they're 2 or more.

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Space Enthusiast Richard Hendricks --"The engineers, as usual, made a tremendous fuss. Again as usual, they did the job in half the time they had dismissed as being absolutely impossible." --Rescue Party, Arthur C ClarkeMother Nature is the final inspector of all quality.

The Mariner 4 images of Mars were badly degraded by a design-defect light leak. They were salvaged by digital image processing. The 6 bit data was inadequate for lower exposure images and after picture 11 of 21 1/10, the imaged degraded rapidly into digitization contour patterns

The Mariner 6 and 7 Mars images were badly degraded by analog tape recorder noise (the oxide flaked in flight and accumulated on the tape-heads), and electronic interference noise patterns, together with considerable geometric distortion of the images, severe shading across the images and bad residual images.

The Mariner 9 images were all-digital once the vidicon image was readout, but the cameras still had distortion, shading, and severe residual image problems. In addition, the color filter wheel stuck some 70 days into the mission, ending up at a polarized-orange position which was acceptible, but didn't help. The narrow angle camera also had severe defocus in images that had high exposure levels (not saturated)

Mariner 10 (Venus-Mercury) fixed the residual image problem by putting lightbulbs INSIDE the camera to create a uniform saturated-frame residual image (after the saturated frame was erased), permitting for the first time reasonable decalibration of the images, but the cameras had real problems with dust specks and lint shadows, and the spacecraft stability was inadequate for the narrow field of view, causing severe pointing wander. Look at Mercury flyby-2 mosaic segments for example. The real time 100,000+ bits/sec communication (experimental) was barely adequate at Mercury so the majority of images (other than the relatively few that could be taped for later playback) had severe salt-and-pepper noise.

Viking orbiters used twin cameras with silicon vidicon detectors instead of selenium-sulfer vidicons (I believe). The data storage system couldn't handle the 2 second (approx) raw readout rate from one camera while the other was taking an image in a rapid-fire left-right-left-right sequence for 50 meter/pixel landing site mapping from periapsis. The 7 bit (inadequate... orbiter images often have digitization contouring) data were split into several pixel channels and dumped in parallel tracks onto the tape recorder, which were then read out sequentially. Pictures (and there were many) where all tracks didnt' make it back to earth are missing columns of pixels in varying amounts which have to be filled in by interpolation. The zero-level of the camera ended up negative, instead of small positive numbers, so a blank exposure of black space was all ZERO's, and it was impossible to directly measure the dark-image shading of the cameras. Inflight calibration of shifts in the camera shading was difficult and generally inadequate. As each picture was being readout the other camera was shuttering it's exposure, then resetting the shutter. The mechanical shutter slap vibrated the cameras, resulting in a series of sine-wave interference patterns for a number of lines in the other camera's image, one near the bottom of the frame, one near the top.. due to "microphonic' vibrations of the photocathode in the camera that was beign read out.

Voyager's cameras were again selenium-sulfer vidicons, using the same lens as Mariner 10 for the narrow angle camera (with improvements). Dust specks were minor, calibration techniques reasonably well worked out. The cameras could be operated with light flood on for optimum calibration, or light flood off for low-light-level sensativity. Inflight calibration between encounters greatly helped maintain decalibrated image quality, though a lot of the cal data has annoying levels of bit errors and missing lines etc, and I had poor luck using the calibration target images to decalibrated flat-field shading from Voyager images (they had an aluminum plate they could get sunlight on by reorienting the spacecraft and then point cameras and other instrumets at). Image stability and pointing was better than Mariner 10's but still less than ideal. Stability was improved after Saturn for the extended mission by reprogramming the attitude control system. The vidicon cameras still had a problem with image distortion, and the images are literally "stretched" toward bright objects by a pixel or two due to electron-beam deflection by the charge pattern on the vidicon surface. This made truely precise geometric measurements in navigation images and the like quite difficult. CCD utterly don't have that problem!

but: "The sad thing about the optical calibration issues that appear to be cropping up on so many current/future missions is that 35 years ago, they had the thing done and dusted"... Uh.. done and dusted?.. no way!

but: "The sad thing about the optical calibration issues that appear to be cropping up on so many current/future missions is that 35 years ago, they had the thing done and dusted"... Uh.. done and dusted?.. no way!

More accurately, most IMAGES we see now from these missions have been dusted

I take the point regarding the steep learning curve on past missions - but it doesn't change the fact that nowadays the problems are known yet dumb mistakes keep getting made. I have every sympathy if it happens once, but after the Hubble mirror fiasco (and it's expensive recovery, for which all credit to those involved) you'd think that the word 'focus' would be at the forefront of everyone's mind...

Bob Shaw: "... but it doesn't change the fact that nowadays the problems are known yet dumb mistakes keep getting made. "

AMEN.

I think it was a BAD mistake not to have a coarse focus adjustment on the deep impact camera.

A big "Uh... I thought we knew about this..." problem... Stardust had a massive problem with condensate from outgassed crud fogging the optics. The earth-flyby image of the moon was 90% fog and 10% image.... massively blurred. Repeated heating of the camera to degass the optics got most of it, but I'm not at all sure they ever did get all of it and the Wildt comet flyby pics I think are somewhat degraded by it. NEAR's optics were significantly fogged by hydrazine byproducts during the loss-of-control event at the first arrival burn attempt that nearly lost the mission (not the camera's fault), and Cassini has had significant fogging problems between Jupiter and Saturn that I think still has some residual that makes it impossible to search for low brightness outgassing plumes at Enceladus.

Fogged optics seem to be the other problem-of-the-decade, besides out of focus cameras.

Bob Shaw: "... but it doesn't change the fact that nowadays the problems are known yet dumb mistakes keep getting made. "

AMEN.

I think it was a BAD mistake not to have a coarse focus adjustment on the deep impact camera.

I don't know all the details of the DI story, but I don't think you guys are being completely fair here.You might recall that in the "old days" cameras had all-metal structures and masses of over 50 kg. For example, the Cassini ISS mass is about 58 kg, fully 4x heavier than the MOC on MGS with its graphite-epoxy optical structure. But for that mass savings, you have to work with a much trickier material. To say that all of the problems are known at this point is not really accurate.

You can usually assume that with optics, even mistakes that seem dumb with 20:20 hindsight are fairly subtle and hard to avoid once you appreciate all the details.

As for focus adjustment; it may be nice to have, but it's heavy and complex and if it fails, you can easily be worse off than before. We studied this trade very carefully for MRO CTX and ended up with no focus adjustment, and we intend to do the same for our LRO instruments. The MOC has focus control heaters, by necessity, but they have only a fairly limited adjustment range. See Ravine, M. A., et al., Graphite-epoxy optical systems: lessons learned on the way to Mars, Proceedings of the SPIE, 5179, 311-322, 2003.

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Disclaimer: This post is based on public information only. Any opinions are my own.

I don't know all the details of the DI story, but I don't think you guys are being completely fair here...

I'm sure you're right (and closer to the subject matter, too!). But (and it's a big but) if graphite-epoxy structures have inherent problems, but are lighter, and metal structures are well-understood, but heavier, then that strikes me as being an excellent argument for 50Kg heavier spacecraft! The MSS kit has all worked well so far, and we all hope that it will continue to do so, but there's no virtue in weight loss if something then fails to perform - it's not as if there was a production line of interplanetary spacecraft and another could just be tweaked and slotted into the cycle for the next launch window!

There *have* been some dumb mistakes, and I'm sure that some technological adventures have also - in hindsight - appeared less than sensible, although they seemed like good ideas at the time. And there have been some technological innovations which have been utter triumphs, too!

The fact remains that what appear to be 'no-brainer' errors are bad for everybody, even if the root cause is subtle and unexpected and actually nobody's fault. The folk who fund (or try not to fund) our toys shouldn't be given any free ammunition with which to shoot 'em down, and words like 'out of focus' or 'basic errors in arithmetic' are way too easy for them to grab hold of. Those guys don't do subtle...

The Deep Impact defocus problem has distinct similarities to the Hubble problem. Tester malfunction, and not enough independent testing to catch the error. Granted, the Deep Space camera was assembled out of focus so that as the structure degassed, it would drift into focus, but images of real objects at or near infinity are remarkably good targets for a final check on optics... even if you only measure the defocus independently. (granted, it's not easy to get images of objects at infinity from a cleanroom)

Sadly, the noise added to the Deep Impact images will probably render multispectral imaging of the nucleus useless due to noise amplification during the deconvolution process. There may well be no usable color information with the original s/n of the camera, but all we may now see is the brownish overall color described in postings from the DPS meeting.

The folk who fund (or try not to fund) our toys shouldn't be given any free ammunition with which to shoot 'em down, and words like 'out of focus' or 'basic errors in arithmetic' are way too easy for them to grab hold of. Those guys don't do subtle...

Amen, brother. Amen.

For want of a better term, the lawyers who decide on the fundings for these things think of them all as "rocket science." That's a paradigm statement for something that only a few people really, truly understand. If rocket scientists get it *wrong*, then it's got to be so hard to understand that maybe we shouldn't spend good money on it, eh?

Yeah -- let's not give the lawyers more ammunition than they already have.

-the other Doug

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“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain

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